The effect of varying impeller geometrical parameters, including impeller type, number of impeller blades, blade pitch angle and blade thickness, on the turbulent velocity fields in mixing tanks has been studied through LDV measurements. Pitch bladed turbines and disc turbines were used in the experiments. It was found that universal time-mean velocity profiles exist for both pitch bladed turbines and disc turbines. Flow number correlations based on power number for both pitch bladed turbines and disc turbines are presented. It was found that there is a link between impeller pumping capacity and the S parameter in the Zwietering correlation, and this can be expressed as N-Q x S = K, where N-Q is the impeller flow number and K is a non-dimensional constant independent of the solid/liquid material property and impeller geometry.